The materials used in this study were four commercial varieties of Egyptian cotton; two (Giza 86 and Giza 90) belonging to the long staple class and the others (Giza 88 and Giza 92) belonging to the extra-long staple category. Within each variety, nine lint cotton grades namely: Fully Good (FG), Good/Fully Good (G/FG), Good (G), Fully Good Fair/Good (FGF/G), Fully Good Fair (FGF), Good Fair/ Fully Good Fair (GF/FGF), Good Fair (GF), Fully Fair/Good Fair (FF/GF) and Fully Fair (FF) were used. Thus Fully Good (FG) is the top quality grade and the others are progressively lower; i.e. Fully Fair (FF) is the lowest grade. Fiber properties were measured by using the Cotton Classifying System Version-5 instrument (CCS-V5). Data collected for the following characteristics were: reflectance degree (Rd %), yellowness degree (+b), trash%, dust%, fiber fragments%, total trash%, No. of neps and Micronaire value.
Mean squares due to all nine grades of long and extra-long staple cotton varieties in combined analysis were highly significant over seasons for all studied characters except yellowness (+b) and fiber fragments% in Giza 92. Highly significant mean performance values of four cotton varieties and nine lint grades for each variety for all studied characters, it became clear that there were significant genetically differences between studied varieties and fiber cotton lint grades within each variety. Gradually increased for yellowness degree, trash%, dust%, fiber fragments%, total trash% (trash, dust, fiber fragments) and number of neps, while gradually decreased for reflectance degree (Rd%) and micronaire value with significant level as transfer for all tested varieties from (FG) grade down to the (FF). All studied varieties showed highly significant negative correlation between fiber cotton grade with yellowness, trash, dust, total trash% and No. of neps, while highly significant positive correlation between fiber cotton grade with reflectance degree and micronaire value. Total trash% and micronaire value as well as reflectance degree and their interactions were the most contributing and influencing of fiber cotton grades. Also these properties and their joint effects are prevailing factors which affect the personal judgment of the grader at evaluating the cotton grade.